Negative type photosensitive compositions which utilize photo-initiated polymerization and photo-initiated cross-linking reaction have been widely used in various kinds of application, for example photoresist, ink and printing plates.
The negative type photosensitive compositions generally contain photopolymerizable polymers or oligomers which have acidic groups, such as carboxylic group, in the structure thereof. Since the acidic groups form salts by treating with an alkaline solution, non-exposed portions are dissolved away when treated with an alkaline solution, while exposed portions are polymerized by photo-initiated polymerization or photo-initiated cross-linking reaction and remain as they are without being dissolved away even though they form salts. However, in fact the exposed portions are slightly dissolved away due to the formation of a salt to "reduce a film-thickness". Such reduction of film-thickness is disadvantageous in respect of sensitivity and image dissolution.